新疆罗布泊K1孔磁性地层及古纬度初析

Magnetostratigraphy and Palaeolatitudes of Hole Kl in Lop Nur, Xinjiang

K1孔位于罗布泊“耳轮”构造的北缘。磁性地层初步研究得知,在孔深61～62 m处为界,以上为布容正向极性时(Br),以下为松山反向极性时(Ma)。在孔底97～100 m处的正向极性偏移应属Cobb Mountains事件,对照S.C.Cande和D.V.Kent修定的古地磁极性年表,孔底地层的年代为1.2 Ma,归属早更新世中期。中更新世地层厚50余米,晚更新世地层厚10 m左右,全新世地层厚度小于5 m。根据古地磁资料计算得知,罗布泊K1孔的古纬度为34.1°。另据库车河剖面和恰恰剖面的古地磁资料计算,它们的古纬度分别为26.7°和20.0°,与现纬度相比,它们的共同特点是都在向北位移,这一规律与印度洋板块和欧亚板块挤压碰撞效应,及塔里木盆地南缘阿尔金断裂的左行走滑运动密切相关。

From satellite images, it may be found that hole K1 is located on the northern margin of the Lop Nur 'helix' structure, at 90. 5°E and 40. 3°N, with an elevation of 780 m above sea level. It is the only hole that has been studied systematically in the Lop Nur region at present. The mag-netostratigraphic study indicates that by choosing the hole depth of 61-62 m as the boundary, the interval above the depth belongs to the Brunhes normal polarity zone (Br) , the interval below the depth belongs to the Matuyama reversed polarity zone (Ma) , and the normal palrity migration at depths of 97 - 100 m on the hole bottom should belong to the Cobb Mountains polarity event. According to the Cande &- Kent geomagnetic polarity time scale, the age of the strata on the hole bottom is 1. 20 Ma, assigned to the middle part of the early Pleistocene. The middle Pleistocene, late Pleistocene and Holocene strata are >50 m, about 10m and <5 m thick, respectively.Calculation of palaeomagnetic data shows that the palaeolatitude of hole Kl of Lop Nur is 34. 1°N. And, according to the calculation of palaeomagnetic data from the Kuche and Qaqa sections, their palaeolatitudes are 26. 7°N and 20. 0 °N respectively. In comparison with the present latitude, their positions have all migrated northwards. This feature is closely related to the com-pressional collision of the Indian and Eurasian plates and the sinistral strike-slip movement of the Altun fault- on the southern margin of the Tarim basin.